On the Web we need to initialize the page for Flutter's consumption, such as load fonts, configure <meta> viewport tags, and so on. Let's call such initialization code an "embedding" of Flutter. We currently have two such embeddings:

• Production embedding: prepares a web-page for running an app normally. This is the embedding you get when you run flutter run.
• Test embedding: prepares a web-page for running a test. The test embedding hardcodes some things irrespective of the actual browser window, such as default to device pixel ratio of 3.0, and replace all fonts with the "Ahem" font.

We need to implement these two embeddings such that user code does not need to altered to run on the web. For example, user-written code should not call ensureTestPlatformInitializedThenRunTest, or webOnlyInitializeTestDomRenderer.